Repeated Acute Stress During the Follicular Phase and Luteinizing Hormone Surge of Dairy Heifers

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Abstract
Seven Holstein heifers were subjected to 15 min periods of stress 2 times per day for 3.5 days during the follicular phase of the estrous cycle. In 2 of 7 trials, stressed animals had no preovulatory surge in luteinizing hormone [LH] whereas in control experiments all 7 had surges. Peak LH concentrations in the 5 animals having surges, and basal LH concentrations in all 7 animals, were unaffected by treatment. Estrous behavior also was unaffected by stress, and all animals displayed estrus during treatment. The 24 h pattern of corticosteroids of plasma was unaffected by treatment; however, there was a significant brief elevation in corticosteroids following stress. Brief stress apparently can disrupt the preovulatory LH surge in the cow and this effect may have significant implications for dairy management.